So I have a player who has a build...

Elf, Cleric, Tempest Domain & Lathander(as their Diety)

Is that a very confused build in relation to lore, Tempest Domain includes Talks which is the opposite of Lathander 

Is there an logical explanation for this build storywise

Lathander doesn't grant Tempest to anyone (elves or otherwise) he'd more be Light/Life.

Does it have to be Lathander? There are elven deities that would grant Tempest, like Aerdrie Faenya, or nature deities like Akadi or Auril.

Its one of my player builds I'm just trying to understand what would make sense without homebrewing alterations within the lore

So ask the player why he thought it was. Good match. They should know better than we we can guess.